Power bank



FIG. 1 is a perspective view of a power bank, showing my design;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines in the drawings are for the purpose of illustrating portions of the power bank and form no part of the claimed design. 

CLAIM The ornamental design for a power bank, as shown and described. 